MINERALOGY OF THE BOCAIUVA IRON METEORITE: A PRELIMINARY STUDY |
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| Authors: | C Desnoyers M Christophe Michel-Levy IS Azevedo RB Scorzelli J Danon E Galvo da Silva |
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| Institution: | C. Desnoyers,M. Christophe Michel-Levy,I.S. Azevedo,R.B. Scorzelli,J. Danon,E. Galvão da Silva |
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| Abstract: | The Bocaiuva iron contains 10 to 15% by volume of silicate inclusions which are surrounded by kamacite (6.5 wt % Ni). The metal shows a Widmanstätten pattern in metal areas devoid of silicates; taenite evolved in plessite fields. The silicate inclusions occur as nodules, and as irregular or chain-like aggregates in which olivine may be rounded or faceted. The magnesian silicates (forsterite, enstatite, diopside) are similar in composition to those of the group IAB irons, whereas the interstitial plagioclase is much more calcic (An 50) than that usually found. Iron sulfide occurs as pyrrhotite and contains 1–2 wt% Cu. Chromite and euhedral magnetite are accessory phases always associated with pyrrhotite. Some patches of pyrrhotite enclose rounded chromite and small plagioclase crystals displaying compositions different from those of the ground mass of the inclusions. Schreibersite shows a compositional variability. This preliminary study underlines the unusual nature of Ms iron and raises several questions concerning the genetic relations between silicates, sulfide and metal, and the thermal history of the whole material. |
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